MA818
RST
CS
MOTEL
INTERFACE
8
BUS
CONTROL
RED PHASE
PULSE
DELETION
PULSE
DELAY
CIRCUIT
RPHT
RPHB
SYSTEM
BUS
AD
0
-AD
7
BUS
DEMULTIPLEXER
R0
R1
R2
R3
R4
24-BIT
INITIALISATION
REGISTER
PHASING
AND
CONTROL
LOGIC
YELLOW PHASE
PULSE
DELETION
PULSE
DELAY
CIRCUIT
YPHT
YPHB
24-BIT
CONTROL
REGISTER
BLUE PHASE
PULSE
DELETION
PULSE
DELAY
CIRCUIT
BPHT
BPHB
CLOCK
CLOCK
DIVIDER
ADDRESS
DATA
GENERATOR BUFFER
11
4
TRIP
LATCH
TRIP
A
0
-A
10
D
0
-D
3
TO
FROM
WAVEFORM STORAGE
PROM/EPROM
SET
TRIP
Fig. 2 MA818 internal block diagram
FUNCTIONAL DESCRIPTION
An asynchronous method of PWM generation is used with
uniform or ‘double-edged’ regular sampling of the waveform
stored in the PROM/EPROM as illustrated in Fig.3. The use of
an external PROM/EPROM allows the user to define the opti-
mum power waveform for the particular motor being used.
The triangle carrier wave frequency is selectable up to 24kHz
(assuming the maximum clock frequency of 12.5MHz is used)
enabling ultrasonic operation for noise critical applications.
Power frequency ranges of up to 4kHz (with 12.5MHz clock) are
possible, with the actual output frequency resolved to 12-bit
accuracy within the chosen range in order to give precise motor
speed control and smooth frequency changing. The output
phase sequence of the PWM outputs can also be changed to
allow both forward and reverse motor operation.
PWM output pulses can be ‘tailored’ to the inverter character-
istics by defining the minimum allowable pulse width (the MA818
will delete all shorter pulses from the ‘pure’ PWM pulse train) and
the pulse delay (underlap) time without the need for external
circuitry. This gives cost advantages in both component savings
and in allowing the same PWM circuitry to be used for control of
a number of different motor drive circuits simply by changing the
microprocessor software.
Power frequency amplitude control is also provided with an
overmodulation option to assist in rapid motor braking.
An asynchronous trip input allows the PWM outputs to be
shut down immediately, overriding the microprocessor control in
the event of an emergency.
Other possible MA818 applications are as a 3-phase wave-
form generator as part of a switched-mode power supply (SMPS)
or of an uninterruptible power supply (UPS). In such applications
the high carrier frequency allows a very small switching trans-
former to be used.
MICROPROCESSOR INTERFACE
The MA818 interfaces to the controlling microprocessor by
means of a multiplexed bus of the MOTEL format. This interface
bus has the ability to adapt itself automatically to the format and
timing of both MOTorola and IntEL interface buses (hence
MOTEL). Internally, the detection circuitry latches the status of
the DS/RD line when AS/ALE goes high. If the result is high.
Then the Intel mode is used; if the result is low then the Motorola
mode is used. This procedure is carried out each time that AS/
ALE goes high. In practice this mode selection is transparent to
the user. For bus connection and timing information refer to the
description relevant to the microprocessor/controller being used.
Industry standard microprocessors such as the 8085, 8088,
etc. and microcontrollers such as the 8051, 8052 and 6805 are
all compatible with the interface on the MA818. This interface
consists of 8 data lines, AD
0
- AD
7
(write only in this instance),
which are multiplexed to carry both the address and data
information, 3 bus control lines, labelled WR,RD and ALE in Intel
mode and R/W, DS and AS in Motorola mode, and a Chip Select
input. CS, which allows the MA818 to share the same bus as
other microprocessor peripherals. It should be noted that all bus
timings are derived from the microprocessor and are independ-
ent of the MA818 clock input.
3
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
